Project Summary: Pulmonary arterial hypertension (PAH) is a lethal disease that affects ~4 times as many women as men. Ironically, female patients fare better than male patients; women with PAH live 2 years longer than their male counterparts. Patient responses to existing PAH therapies also vary depending on sex. These gender disparities in PAH may stem, at least in part, from intrinsic differences between the two sexes and from the conflicting roles of sex hormones, especially estrogen. Estrogen increases the pathologic proliferation of pulmonary arterial smooth muscle cells, but it also protects against right ventricular hypertrophy (RVH). The role of the male sex hormone testosterone in PAH is poorly defined but it appears to have a part in promoting RVH in men. Progress in understanding the sex- disparity in PAH has been slow, primarily because of the lack of experimental models that can recapitulate human PAH in its sex-specific forms. Existing animal and cellular models, while having aided in addressing many important questions, do not accurately portray the sex-related variability in PAH development and progression, nor are they sufficiently malleable for certain mechanistic studies. A human tissue-chip model of PAH?able to capture its sex- specific disease etiology, reproduce PAH-induced RVH, and simulate sex-specific responses to drug therapy? could provide a much-needed breakthrough in understanding the mechanism of the sex disparity in PAH and lead to improved treatments for PAH patients. Recently, we designed and fabricated such a device, a state-of-the-art microfluidic tissue-chip that mimics the five layers of the pulmonary artery (perivascular, adventitial, medial, intimal and luminal), both normal and diseased. Further, in preliminary studies, we demonstrated that our tissue-chip can recreate PAH-afflicted pulmonary arteries, emulate the severity of the disease, and model the differences in the therapeutic response of male versus female patients. Here, we propose to deploy our new device to study the pathophysiology of different forms of PAH, investigate the influence of sex and sex hormones on development and progression of the disease, and assess the relative efficacies of mono and combination therapies in both sexes. We will also modify the chip to reconstruct PAH-induced RVH to study how intercellular communication between cardiac cells and cells of PAH-afflicted pulmonary arteries contributes to the pathology, and evaluate the effect of drugs on PAH-induced RVH. This is an exceptionally innovative project with far-reaching clinical significance, as it combines the power of microfluidic technology with the flexibility of combinatorial study design to elucidate the pathomechanism of PAH in both women and men. The investigative team, comprising a pharmaceutical scientist with a longstanding interest in PAH, a chemical engineer, an expert in microfluidic technology, two physician scientists, and a PAH biologist, is highly qualified to conduct this study. If successful, this tissue-chip model may revolutionize approaches to studying sex-based pathophysiology and therapy for vascular diseases, and enable clinicians to develop personalized therapies for their PAH patients.